Method of stirring dispersing or homogenizing metal or slag charges having a temperature of at least 800deg. c.



Oct. 11, 1966 JAN-ERIK OSTBERG ETAL 3,278,295

METHOD OF STIRRING DISPERSING OR HOMOGENIZING METAL OR SLAG CHARGESHAVING A TEMPERATURE OF AT LEAST 800C Filed Aug. 10, 1964 INVENTORSJAN-ERIK OSTBERG SVEN GYNT LARS GYNT AKE SAHLBERG United States Patent3,278,295 METHOD OF STIRRING DISPERSING 0R HOMOG- ENIZING METAL 0R SLAGCHARGES HAVING A TEMPERATURE OF AT LEAST 800 C. Jan-Erik Ostberg,Bettua, Sven Gynt and Lars Gynt, Vasteras, and Ake Sahlberg,Halsingborg, Sweden Filed Aug. 10, 1964, Ser. No. 388,397 (Ilaimspriority, application Sweden, July 7, 1960, 6,627/60 1 Claim. (Cl. 7561)This application is a continuation-in-part of our application Serial No.119,548, filed June 26, 1961, now abandoned.

The present invention relates to a method for stirring, dispersing orhornogenising metal or slag charges having a temperature of at least 800C. with one or several phases to which is possibly added material insolid, liquid or gaseous form and in which a physical process is desiredeither within one of the phases or between these. The invention alsorelates to a mechanical device for performing the said method.

A problem which often arises within this technique concerns homogenizinga fluid or combining two or several fluids with each other. This isespecially so in the metallurgical industry. The precautions taken withraw products or semi-finished products are very often marked by the factthat they immediately influence only one part of the system or the batchof material being treated. The actual process, therefore, wouldcompletely or partially fail if the effect could not be successfullyspread over the whole quantity of material.

This can be illustrated by some practical examples. When vacuum treatinga metal charge only a very insignificant outer layer is influenced,which is in direct contact with the evacuated space. charge wouldcompletely escape the influence of the low pressure if it were notsuccessfully transported up to the surface just mentioned. Thiscircumstance is connected with the heating. Only that part of the metalcharge which is directly subject to the influence of an arc, flame orheat radiating surface, is heated immediately. In order that the actualprocess may take place sufficiently rapidly, it is often a conditionthat the heat, by means of stirring or some other type of forcedconvection, is transported further to other parts of the charge. Anothertypical problem of this type arises when the percentage of some alloyingmaterial is to be increased by means of a suitable addition to a chargeof alloying material in solid form. While the solid alloying materialmelts and dissolves, only that part of the charge is influenced which isin direct contact with the alloying material. Finally, as an example ofhomogenizing it should be established that, in such metallurgicalreactions which consist of an exchange of material between a metalcharge and a slag, it is generally a very small part of the whole systemwhich is directly influenced by the reaction. Particularly when it is aquestion of a demand for high reaction speed and reaching relativelycompletely equal thermodynamic equalizations, it is necessary toequalize the compositions and temperature dissimilarities which are theresult of the material conversion which takes place at the boundarylayers where the different phases meet.

When such problems arise on a small scale it may be suflicient to takesome simple manual steps such as shaking or agitating or utilizing somesimple hand tool. On the other hand, when it is a question of work on alarge scale, when a certain pattern of movement is aimed at, when it isdesired to maintain clear phase boundaries and when it is desired toscreen off the space above the charge in order to maintain a vacuumthere or a particular type of atmosphere, a mechanical device must beused. The

The main part of the "ice stirring, dispersing and homogenizingoperations outlined above are of course of a transitory nature, but theyall have in common that their completion cannot be brought abouteffectively without a rapid movement being created in the charge, themovement including the whole or the greater part of the charge and beingpreformed with a minimum of turbulence.

The problem in this connection might also be expressed as a desire toobtain a closed pumping circuit or streaming circuit in which thestreaming occurs regularly and according to a certain pre-determinedmovement, and in which acceleration power is introduced in the chargeaccording to a part or along the whole length of the circuit. Goodresults have been obtained with the so-called electro-dynamic stirrer,but this solution is relatively expensive, as is the so-called vibratoryladle also. In .both these cases, the forces which set the charge inmotion automatically guide them in regular streaming circuits.

The invention relates to a method producing both an effective andeconomic solution to the above mentioned problem and is characterised inthat the charge (temperature at least 800 C.) completely or for the mostpart is given a streaming movement by means of a mechanical device atleast partly lowered in the charge, whereby the said device whilerotating with respect to a surrounding vessel containing the charge witha speed of at the most 500 r.p.m. guides the streaming of the chargepartly along a substantially horizontal, partly along a substantiallyvertical path of movement, the total path of movement within the deviceper streaming revolution for each stirred part of the charge being atleast 15% of the sum of the average height and the average diameter forthe whole charge. At the same time a good stirring is obtained accordingto the above mentioned requirements. The invention also includes amechanical device for performing this stirring. This mechanical deviceis characterized in that it is formed of a substantially vertical tubeand one or more side tubes placed at an angle and communicating with theupper part thereof, in which the total length of the vertical tube fromoutlet opening to longitudinal axis of a connecting tube and the lengthfrom this tube from the longitudinal axis of the vertical tube to theoutflow opening is at least 15 of the total maximum average fluid heightand maximum average fluid diameter in the ladle or the vessel in whichthe device is intended to be lowered.

The advantages of this device, as also certain further advantages withthe above indicated method according to the invention will be seen moreclearly from the follow ing description taken together with theaccompanying drawings which form a part thereof.

In the drawings:

FIG. 1 shows a ladle with the stirrer in section according to theinvention.

FIG. 2 is a cross-section on the line 2-2 of FIG. 1;

FIGS. 3, 4 and 5 show modified stirrers in vertical cross-section.

In the vessel of FIGS. 1 and 2, which constitutes a ladle 1, is a charge(temperature over 800 C.) covered by slag. Into the charge is lowered astirring device 2. This device consists of a cross-bar fixed in avertical shaft 3 which is driven by the gear 4 of the motor 5. The motorand gear are parts of a single construction which in its turn is held bya lid 6 placed on the vessel 1. The lid is provided with sealings at 7and 8. As is clear from the figures, the stirring device is formed of avertical pipe section, and on this are rigidly fixed one of severalhorizontal tube connections or lateral pipes 9, usually shorter than thepart of the vertical tube below each horizontal lateral pipe, theinteriors of which communicate directly with the interior of the tubesection. The vertical pipe section is closed at the top.

The laterally extending pipes are angularly spaced apart and thus havelateral side walls 11 which exert a stirring action on the charge.

As mentioned, the stirrer should rotate with a speed of at the most 500r.p.m. and the sum of the length b of the vertical pipe section belowthe longitudinal axis of the lateral pipes and the distance a from theouter end of the horizontal tube part to the longitudinal axis of thevertical part should be at the most 15% of the sum of the maximumaverage fluid diameter d and the maximum average fluid height h of thecharge. These limitations are of importance in order to achieve therequired stirring and at the same time limit the wear on the stirrer.The provision may also be made that, with relatively insignificanthorizontal guiding, at least 25% of the maximum average liquid heightshould be guided vertically and at least 25% of the maximum averagefluid diameter should be guided horizontally with relatively shortvertical guidance. Furthermore, the distance b should be at least twice,and preferably at least three times, the internal diameter e of the pipesection 2.

A vacuum can be produced within the ladle by pump P.

One of the many advantages with the present stirrer is that the pump(the stirrer) as such rotates, but relative movement between the pumpdevice and the guiding device is avoided since both these devices areinstead constructed as a unit. The pump is further built on theprincipal known per se of operating the pump by allowing the fluid toaccelerate in a tube arranged at an angle to the rotating shaft. Theguiding is obtained by giving the tube the required length.Characteristic of the invention is further that the pump, by rotating,places that pump nearest the surrounding charge in rotating movement.Since the pump is made large in comparison with the surrounding fluid,it can be constructed for moderate rotation movements. Even withmoderate speeds of rotation such great centrifugal speeds are reached inthe outlet of the horizontal tube connections that the device willoperate as an effective pump which draws in fluid at the inlet of thevertical tube and pumps it out of the mouthpieces of the horizontaltubes; The stirring takes place partly on account of pump action, partlyon account of moving parts of the charge by the action of the side wallsof the protruding side hook arms.

It is of course unnecessary for the rotating shaft to be completelyvertical. The movement can also be altered in a number of other ways.The inlet can thus be placed in the upper section of the vertical tube.The pump can be placed more or less eccentrically in the vessel.Finally, the horizontal tube connections can be made shorter or longer.They could be directed somewhat upwards or downwards and of course beplaced at different heights in the vessel.

The apparatus also has the advantage that additions in solid, liquid orgaseous form can be made to the streaming fluid. The additon can be madein such a way that only the immediately pumped fluid is influenced andcan easily be modified so that the walls of the pump are not influenced.

The pump which is shown in the figures is constructed for use with aniron ladle, for example of a type containing tons. It operates with aspeed of rotation of approximately one revolution per minute and, withan inner tube diameter of 150 mm., gives such a great capacity that thecomplete iron content passes through the vertical aird horizontal tubesof the pump. On this movement is superimposed a horizontal rotationbrought about by the si-defaces of the horizontal branch tubes. Despitethe fact that the pump operates with very low speeds, so that themechanical stresses on it will be very low, a rapid mixing is thusobtained in accordance with one pattern of movement, which can be variedwithin wide limits.

These circumstances are important if the problem is to be solved bymeans of a mechanical aid in surroundings where stresses of temperature,temperature shocks and chemical actions are severe. Without such asimple construction that the thickness of the material does not fallbelow 10 mm. at any position and that neither do any radii fall belowthis measurement, the stirrer cannot be sufiiciently stable for work inmetal charges or slagsv For the same reason the speed of rotation, asmentioned above, should not exceed 500 r.p.m. and the speed of the fluid5 m. per second.

The tube is manufactured according to any known method and of anymaterial which is durable in the specific conditions. With crude iron,graphite is often the best solution. If the carbon percentage is too lowor with steel, schamotte may be chosen instead which at hightemperatures may be replaced by special schamotte or sillimannit. If thedimensions and speeds are kept within the specified limits the choice ofmaterial will not be difficult.

In the modification of FIG. 3, a single lateral or side tube 9a isshown.

In FIG. 4, lateral pipes 9b are arranged at the bottom, and pipe section2 has openings 10 at its upper end. The flow direction is the reverse ofthat shown in FIG. 1.

As shown in FIG. 5, lateral openings 100 instead of a downward openingmay be provided for pipe section 2.

The stirrer according to the invention and the method of stirring, etc.,likewise according to the invention may be varied in many ways withinthe scope of the following claim.

I claim:

A method of stirring charges of a temperature of at least 800 C. with atleast one phase in a vessel, in which materials are added to the chargein order to obtain physical processes in at least one phase, whichcomprises immersing into said vessel, and at least partly into saidcharge, a mechanical stirring device comprising a depending drivingmember having at its lower end a vertical pipe section and at least onelateral pipe extending out from said pipe section and having exposedside walls so that one side wall exerts a stirring action upon rotationof the stirrer, the interior of the lateral pipe communicating directlyat its inner end with the interior of the pipe section, said pipesection having an opening therein remote from said pipe and beingotherwise closed, said pipe section and lateral pipe together forming avertical and outward flow path; the length of vertical pipe sectionbetween said opening and the point of communication of the lateral pipebeing at least twice the internal diameter of the vertical pipe sectionrevolving said stirring device at a speed of not more than 500 r.p.m. inrelation to the vessel to cause streaming movement in at least thegreater portion of said charge, the path of movement of each stirredportion of the charge in its passage through the vertical pipe sectionand lateral pipe being at least 15% of the sum of the mean height andmean diameter of the whole charge.

References Cited by the Examiner UNITED STATES PATENTS 1,311,964 8/1919Grosvenor. 2,397,737 4/1946 Heuer -55 2,660,525 11/1953 Foster 75--773,893,860 7/1959 Lorenz 7549 OTHER REFERENCES The Iron Age, Nov. 2,1939, p. 55.

BENJAMIN HENKIN, Primary Examiner.

